Sound suppressors are mounted onto firearms to control the expansion of muzzle gases to reduce the sound intensity of the shots fired. The reduction in sound can aid in reducing hearing damage to the shooter and reduce noise to avoid disturbance to others in the vicinity of the shooter. The suppressor may also reduce muzzle flash, and thus aid in concealing the location of the shooter. The sound suppressor secures onto the barrel of the firearm, typically via a threaded connection, and encloses a baffled interior space into which the muzzle gases expand. The baffled interior is configured to control expansion of the muzzle gases to reduce the resulting sound intensity.
It has been found that the first shot fired through a sound suppressor frequently is louder than following shots, due to the hot muzzle gases burning in the oxygen contained in the residual air in the baffled interior space. This is frequently referred to as “first round pop” or FRP. To avoid this additional noise, users may attempt to inject a non-flammable gas such as carbon dioxide (CO2) from a source of compressed gas into the suppressor to displace the residual air. Since this operation is typically conducted while a live round is chambered, it requires the user to place their hands in proximity to the exit of the suppressor, in line with the muzzle, to inject the gas; this creates an inherently unsafe condition, as well as being inconvenient.